1. Field of the Invention
The present invention relates to an attachment structure for attaching a solid-state imaging device to each color light exit end of a color-separating prism. More specifically, it relates to an attachment structure for a solid-state imaging device for attaching the solid-state imaging device to a color-separating prism by using an adhesive.
2. Description of the Prior Art
Color-separating prisms for decomposing object light from an imaging lens into a plurality of wavelength region components and outputting thus obtained components have conventionally been known in video cameras and the like. Solid-state imaging devices corresponding to individual color light components are attached to the respective color light exit ends of such a color-separating prism, so as to receive their corresponding color light components from the exit end faces.
When the solid-state imaging devices receive light in this case, it is necessary that the superposition of objects in different colors, i.e., registration, be carried out at a high accuracy in order to prevent color misalignment, moiré, and the like from occurring. In particular, along with the recent tendency of solid-state imaging devices to attain a greater number of pixels, their pixel pitch has been decreasing remarkably, thus requiring a severe positional accuracy, which makes it necessary to attach the solid-state imaging devices to the color-separating prism while in a state securely positioned.
While a technique disclosed in Japanese Utility Model Publication No. HEI 3-14872 and the like has been known as prior art, it is desirable that the light exit end face on the color-separating prism side and the light entrance face on the solid-state imaging device side be directly bonded to each other with an adhesive when the easiness of attaching operations is important.
In the case of direct bonding with the adhesive, small bubbles and dust particles mixed into the adhesive exist within a region through which an incident luminous flux onto the imaging section of the solid-state imaging device passes, whereby captured images deteriorate greatly. When attaching the solid-state imaging device to the color-separating prism, it is necessary for individual color object images to be superposed at a high accuracy as mentioned above. Therefore, for example, they are held with a 6-axis adjusting jig or the like so as to oppose each other in a predetermined posture with a predetermined gap therebetween. Thereafter, a UV-curable adhesive or the like is injected throughout the gap and is cured upon UV irradiation, whereby the possibility of bubbles and the like once mixed into the adhesive being released is low. However, since bubbles as small as about 10 μm may still affect the image quality severely, it is hard for the above-mentioned technique to maintain the quality of captured images favorably.